Method of accurately measuring volume of injected metal in forming core elements for lost core molding process

ABSTRACT

An improved method for forming cores to be utilized in a loss core plastic molding process includes the use of a flow meter. The flow meter ensures that sufficient molten metal is delivered into a cavity for the loss core elements. In this way, the present invention eliminates the occurrence of gaps, spaces or cavities in the molded loss core part. Most preferably a magnetic flow meter is utilized which can monitor the amount of molten metal having flown through the flow meter.

[0001] This application claims priority to Provisional Patent Application Serial No. 60/242,871, filed Oct. 24, 2000.

BACKGROUND OF THE INVENTION

[0002] Lost core plastic molding techniques are becoming widely utilized in plastic molding operations. In a typical lost core process, metal core elements are initially cast. The metal core elements are preferably formed of a material which has a relatively low melting point. The core elements are then placed into a plastic mold, and plastic is molded around the core elements. The plastic has a relatively high melt point. The core element is then melted, leaving the plastic molded body around a plurality of cavities where the core elements had been. Loss core molding techniques are becoming popular in that they provide a way of forming intricate surfaces on the interior of a plastic molded part.

[0003] There are challenges with the use of loss core molding, and in particular with the formation of the core element. For the core element to provide an intricate surface within the molded plastic part, the core element itself must have a desired outer surface. It is the outer surface of the core element which forms the interior of the cavity in the molded plastic element.

[0004] In the past, there have been problems with reliably forming the core element. If the core element is formed improperly, then there will be cavities within the core element, and the core element must thus be scrapped. The cavity occurs when an insufficient amount of metal is sent into the core mold cavity. There are other problems when too much metal is sent into the cavity. Either of these occurrences result in a scrapped part, which is undesirable.

[0005] In the prior art, a pump for moving the molten metal into the cavities in a core mold has been monitored. The amount of movement in a piston in the pump has been utilized to provide feedback of when sufficient metal has been moved. This process, however, still results in the underfill and overfill problems as mentioned above.

SUMMARY OF THE INVENTION

[0006] In the disclosed embodiment of this invention a flow meter is placed adjacent to the cavity in the core mold. Preferably, the flow meter is a magnetic flow meter and is responsive for identifying the velocity of the flowing metal through a conduit associated with the flow meter. By knowing the cross-sectional area and the velocity an easy determination can be made of the quantity of molten metal that has moved into a particular cavity. The quantity is compared to an expected quantity, and one of two processes can be utilized.

[0007] In a first most basic process if the metal flow stops while there is insufficient metal flow, then a warning signal can be created. In a second embodiment, a control further controls a nozzle valve. The nozzle valve is controlled to close when the flow meter identifies that a correct amount of molten metal has moved into the cavity. Thus, the nozzle will close prior to any overflow and will not close until there is sufficient metal. In this fashion, the present invention ensures that the core will have sufficient material such that the core will be properly formed.

[0008] Once the core is formed, it is placed into a plastic mold and it is utilized as part of a lost core molding process.

[0009] These and other features of the present invention can be best understood from the following specification and drawings, the following which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 schematically shows a core molding process.

[0011]FIG. 2 schematically shows a plastic molding process.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0012] A system 20 is illustrated for molding loss core elements in a loss core mold 22. As shown, a plurality of cavities 24, 26 and 28 are formed within the mold 22. A molten metal supply 30 is provided with a pump 32 and controlled by a control 34. A supply conduit 36 communicates with the cavity 28, and similar conduits 36 communicate with the cavities 24 and 26. The conduits 36 are each associated with a nozzle valve 38 which is controlled both to close flow through the conduits 36 and a flow meter 40. While various types of flow meters may be utilized, most preferably, the flow meter is a magnetic flow meter which is able to sense the velocity of molten metal flowing through the conduit 36 due to the magnetic properties of the metal. The control 34 takes in feedback about the velocity of the metal through the conduit 36. The control 34 is further programmed to know the cross-sectional area in the vicinity of the flow meter 40. By knowing velocity and cross-sectional area the control can estimate with extreme accuracy the amount of liquid metal which has moved into any of the cavities. The control 34 is further programmed to know the desired amount of molten metal.

[0013] Thus, during the filling operation, the control 34 monitors the amount of molten metal moving into each of the cavities 24, 26 and 28 through the flow meters 40. If the flow of metal has stopped before the desired amount of molten metal has moved into one of the cavities, then a warning signal such as shown at 39 may be actuated. A worker controlling the molding operation will then be able to stop the molding operation prior to the formation of a part that will inevitably be scrapped.

[0014] In a second embodiment, the control 34 in conjunction with the flow meter 40 controls the nozzle valve 38 to ensure adequate flow. The nozzle valve 38 remains open until the desired amount of molten metal has moved into the cavities 24, 26 or 28. At that time, the nozzle is closed. Thus, overfill will not occur. The nozzle remains open until sufficient metal has moved into the particular cavity. Again, the nozzle is controlled by the control 34. While a single control 34 is shown for each of the three cavities, it should also be understood that an individual control module can be associated with each valve and flow meter.

[0015] One preferred magnetic flow meter is available from Endress Hauser.

[0016]FIG. 2 shows a plastic loss core molding operation 50 having a cavity 52. As is known, the core parts 124 and 126 are placed within the cavity 52 and a supply 54 of plastic in injected into the cavity 52 around the core elements 124 and 126. In this fashion, a molded plastic part is formed having cavities of a desired and intricate inner periphery. As is further known, the core elements 124 and 126 are then melted after formation of the plastic part, leaving the cavity.

[0017] The present invention thus provides a way of making the core elements for a loss core plastic molding system more reliably.

[0018] While a preferred embodiment has been disclosed, a worker in this art would recognize that various modifications would come within the scope of this invention. For that reason the following claims should be studied to determine the true scope and content of this invention. 

1. A method of forming a loss core part comprising the steps of: 1) providing a mold for forming a loss core element, said mold having at least one cavity, said cavity desirably receiving a first amount of molten metal to form said element; 2) delivering molten metal into said cavity; and 3) providing a flow meter on a delivery conduit delivering said molten metal to said cavity, said flow meter monitoring the amount of molten metal flowing into said cavity, and said flow meter acting to compare said amount of metal flowing into said cavity to said first amount of molten metal.
 2. A method as set forth in claim 1, wherein said flow meter controls a nozzle, said nozzle being maintained open until a desired amount of molten metal flows into said cavity, said nozzle then being shut.
 3. A method as set forth in claim 1, wherein said flow meter is magnetic, and said magnetic flow meter monitoring the movement of said molten metal through said conduit.
 4. A method as set forth in claim 1, wherein said core elements are then moved to a plastic loss core molding line, and placed into a plastic mold, plastic then being molded around said core elements. 